Flexographic printing plates are relatively expensive compared to other types of plates such as those used in offset printing; therefore, flexographic printers will only use the appropriate amount of plate material necessary to transfer a graphic image. The graphic image is subsequently transferred from the flexographic plate to a substrate such as film, paper, or board, etc. Printers reduce the cost of printing when using flexographic plate material, by not using flexographic material where no graphic elements exist.
Imaging on plates mounted on sleeves requires two major functions:                a) Image wrapping—preparation of an input file, typically presented by a tagged image file format (TIFF). The input file represent a minimal repeat length of repeated graphics imaged on the flexographic plate.        b) Seam definition—preparing the plate/media that will be mounted on the sleeve.        
During the image wrapping a staggered layout 104 comprising a step and repeat element or image element 124 is positioned in various locations across staggered layout 104. The staggered layout 104 is converted into an imageable rectangle 108 as is shown in FIG. 1. The converted imageable rectangle 108 is prepared for further imaging on a computer to plate imaging device.
The imaged data comes in a 1-bit TIFF format 112 from a workflow system. It is cropped and sections are rearranged producing “one-up” artwork 120 after wrapping, to output a rectangular image area that has a height equal to the repeat length 116 (circumference) of the media sleeve.
A sleeve can be supplied either as a continuous sleeve, without a seam, in this case imaging on a single and continuous media which has already been mounted on a sleeve. Alternatively, the sleeve can be supplied with a seam, or discontinuous, such that one or more pieces of flat media are mounted on a sleeve prior to imaging. The media can be mounted as a single piece 204, as shown in FIG. 2, wrapped around the sleeve 208. The media can also be mounted in lanes 212 (strips of media) wrapped around sleeve 208.
A sleeve design software application is useful to design a seam position for a discontinuous sleeve. The seam position defines the shape of the media, which will be cut on a cutting table. The application will also allow a “wrapped view” and a “stitch view” to display the image in various ways to determine the best seam position.
The software application will create:                a) a TIFF File that contains the wrapped data.        b) a cutting table file in an appropriate format such as Common File Format Version 2 (CFF2) for cutting the plate media to conform with the packaging job requirements.        c) mounting instructions that the operator uses to program the pre-mounter and position the media for the stagger. This is a text file containing the sleeve and one-up artwork dimensions, stagger distance, and other job parameters.        
Packaging jobs may differ in seam paths, depending upon the dimensions of the one-up artwork and the stagger in the step-and-repeat pattern. Separations within a job may have different seam paths, depending on the image content of the separation. Seam path can be a straight line or, as shown FIG. 3, a staggered path such as a “castle-top” 304 or “staircase” 308 patterns.
When mounting media to accommodate staggered step and repeat, the seams need to be positioned so that they do not run through an area that will be imaged. One way to do this is to have the seams run along the staggers of the stepped and repeated image, as there is usually no content in the staggered area that would be affected by a seam running through it. FIG. 3 shows a one-piece discontinuous media.
FIG. 4 shows lanes positioned in a staggered manner 404 around sleeve 208. FIG. 5 illustrates a non-staggered artwork 504 configuration and a staggered 508 art work configuration.
The separations within one job do not all have to be mounted in the same manner. In a six-separation job, for example, it may make sense to use continuous media for two separations, single piece media for three separations, and lanes for one separation.
Decisions about media mounting do not need to be made during file preparation. The operator can make decisions on a separation by separation basis just prior to mounting, based on various factors. See below.
MountingoptionsAdvantagesDisadvantagesLanesRectangular pieces of media onlyMore pieces of media to mountPotentially less media used(increased time and risk of errors)Stickyback seams can be aligned withMore difficult to minimize gapsplate seamsacross the drumMany seams to treat (sealing, taping)One pieceRectangular pieces of media onlyDifficult to find a location for astraight seamOnly one piece of media to mountstraight seam in busy separationsFewer seams to treat (sealing, taping)Chance of press bounce if bearer barsStickyback seams can be aligned withare not usedplate seamsOne pieceOnly one piece of media to mountNon-rectangular piece of mediastaggered seamMore continuity in the slow scanincreases likelihood of wasting media(castle-top ordirection (than lanes)staircase)Fewer seams to treat (sealing, taping)
FIG. 6 shows an example of a seam defined by lanes 604. The example shows large non-imaged areas 608, hence calling for lanes configuration. Just the areas defined by lanes 604 will be imaged, therefore a lanes configuration will be optimal for this packaging job, and will yield saving of expensive plate material.
In the case where a single piece of media is the optimal solution, such a configuration is adequate for packaging jobs characterized by imaging content throughout the entire plate. In those configurations it will be still there will be only one seam to describe, but a decision will be required whether the seam will be in a form of castle top 704 or staircase 708 as is depicted in FIG. 7.
A suitable software application may allow the user a full control over the cutting line. The user can move the line while having a full view of the data of the file. Additionally the user may be able to define the path of the line according to visual view on screen.